1. Field of the Invention
The present invention relates to a video and audio synchronization method and related apparatus for a multimedia interface, and more particularly, to a video and audio synchronization method and related apparatus utilizing a boundary between a control period and a data/video period of HDMI serial video and audio data for calibrating and synchronizing timing sequences of data transmission in a plurality of data channels.
2. Description of the Prior Art
With the popularity of digital televisions, DVD display devices, and high definition flat panel displays, the time when people can really enjoy videos with high definition and high quality has finally arrived. However, the mainstream of signal transmission interfaces for flat panel displays is still based on conventional analog interfaces that have limitations of transmission distance and signal bandwidth. Furthermore, the flat panel displays have to convert the analog signals into digital signals through built-in analog-to-digital converters. In this case, not only does there exist a great energy loss in the signal conversion, but the transmission distance is also less than 2 to 3 meters. Therefore, in order to solve the problem, seven companies, including Intel et al., provided a specialized signal transmission interface for digital display devices: Digital Visual Interface (DVI). DVI is utilized for transmitting video signals in digital format to display devices. Since operations such as coding, compression, and error correction can be performed on digital signals, the transmission distance can be extended to 10-20 meters, and high quality images can also be obtained. However, the size of DVI connector is large, and audio signals cannot be transmitted through DVI, so DVI is mainly used for image data transmission between computers and display devices.
Based on DVI, a high definition multimedia interface (HDMI) is a transmission interface specifically designed for next generation multimedia video and audio devices. HDMI is suitable for digital televisions, DVD recorders and players, set-top boxes, and other multimedia electronic devices. Different from transmitting the audio and video signals separately, the most significant characteristic of HDMI is that the video and audio signals are integrated and transmitted together through HDMI. In HDMI, uncompressed digital data transmission is utilized for eliminating signal interference and attenuation effectively in conversion of digital and analog signals. Compared with DVI, not only is the size of HDMI connector smaller, but the audio signals and the control signals for the devices can also be transmitted with the video signals. Furthermore, a high bandwidth digital content protection (HDCP) technique can be added in HDMI for preventing image data from being copied illegally.
Please refer to FIG. 1. FIG. 1 is a schematic diagram of an HDMI transmission and reception system 100. The HDMI interface utilizes a transition minimized differential signaling (TMDS) method for coding, and includes four data transmission channels, three of which (TMDS channel 0 through TMDS channel 2) are utilized for transmitting video and audio data, and the other of which is utilized for transmitting clock data. A display data channel (DDC) is utilized for reading an extended display identification data (EDID) indicating the display characteristics of the receiving end, such as resolution, etc. First, the transceiver 110 converts and synthesizes the video and audio data into a format capable of being received by the receiver 120. The transceiver 110 then encodes the video and audio data by TMDS, converts the video and audio data from parallel format to serial format, and transmits the serial data by low voltage differential signaling (LVDS). Note that, the operation of the receiver 120 is the same as that of the transceiver 110, but the operation sequence is opposite.
Generally speaking, the transceiver 110 outputs respectively the ordered serial video and audio data into the TMDS channels at the same time. However, due to layout or process variation, the length, impedance, gain, and attenuation of each TMDS channel are different, such that the data transmission in each TMDS channel is delayed by a different amount. That is, the timing sequence is shifted by different amounts. In this case, the receiver 120 cannot receive the video and audio data transmitted in the TMDS channels simultaneously. Therefore, in order to enable the receiver 120 to acquire all of the desired video and audio data correctly, it is very important to calibrate and synchronize the timing sequence of the data transmission channels. However, the method and the related apparatus for calibrating the timing sequence of the data transmission channels is not set forth in the HDMI specification and in the prior art.